Remove the null terminator from flask_utils.py

[NEC-Vishal]

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[NEC-Vishal]

#707

[c0c0n3]

@NEC-Vishal we're not there yet... :-)

[c0c0n3]

@NEC-Vishal nice try, but it won't work :-)
In fact, if the input iterable isn't empty the output JSON array will contain an extra comma before the array end symbol, e.g. [1, 2, 3] ~~~> "[\n1,\n2,\n3,\n]" which is not a valid JSON array!

[c0c0n3]

@NEC-Vishal before going ahead w/ this PR, can you please have a read through #707. I realised the TODO in the code isn't really helpful, it's so vague that's basically impossible to understand. #707 now explains the whole thing in detail.

[c0c0n3]

@NEC-Vishal another thing I realised is that if we merged the small change you implemented, the whole WQ query API would break. This is my fault b/c I didn't realise we needed to have test cases to cover the array streaming format. So let's add test cases. Can please create a Python package wq.ql.tests and a file test_flaskutils.py with the following content

import json
import pytest

from wq.ql.flaskutils import *


class Item(BaseModel):
    id: int

    @staticmethod
    def range(stop: int) -> ['Item']:
        return [Item(id=x) for x in range(stop)]


items_array_supply = [
    Item.range(stop) for stop in range(4)
    # [], [Item(id=1)], [Item(1), Item(2)], ...
]


def stream_to_json_doc(xs: Iterable[BaseModel]) -> str:
    lines = [line for line in json_array_streamer(xs)]
    return "".join(lines)


def extract_item_ids(streamed_doc: str) -> [int]:
    item_array = json.loads(streamed_doc)
    return [x['id'] for x in item_array if x is not None]


@pytest.mark.parametrize('items', items_array_supply)
def test_json_array_streamer(items: [Item]):
    want = [x.id for x in items]
    got = extract_item_ids(stream_to_json_doc(items))

    assert want == got

[c0c0n3]

@NEC-Vishal then you should hook up the new tests to the ql suite. If you run the tests in that file against your code that zaps the JSON null value, you should see a JSON decode exception.